Your hand is ready (聽牌) when one more tile would finish five sets and a pair. Knowing exactly which tiles do that decides whether you call a win on the next discard or let it pass, and whether the tile you are about to throw away is one you need. Miss a wait and you give away a win you had already earned; read waits quickly and you can also count how many of your tiles are still live.
How to do it
1.
Split the 16 tiles into finished sets: runs (順子) and triplets (刻子). Most ready hands give four sets and a small unfinished part; some give five sets and a single tile.
2.
Look at what is left over. It is usually a two-tile partial set plus a pair, two pairs, or one lone tile.
3.
List every tile that finishes it: an open run waits at both ends (6-7 wants 5 or 8), a gap waits in the middle (6-8 wants 7), an edge waits on one tile (1-2 wants 3), a lone tile waits for its pair, and two pairs wait on either one.
4.
Check the pair, then split the hand another way. The pair might belong in a run, or a set might serve as the pair; a long run in one suit can be read several ways, and each reading can add a wait. Your waits are everything every split produces.
Five sets are already done: 1-2-3, 4-5-6 and 7-8-9 of characters (萬), then 1-2-3 and 4-5-6 of bamboo (索). A single white dragon (白) is left, and the hand still needs a pair, so the only winning tile is a second 白. This single wait (單吊) is the narrowest there is: at most three 白 are left anywhere.
Two-sided: 6-7 of bamboo waits on 5 or 8
Waits
Four sets are finished: 1-2-3 and 4-5-6 of characters, 7-8-9 of dots (筒) and 2-3-4 of bamboo. The two red dragons (中) are the pair. What's left is 6索 and 7索, a run open at both ends: 5索 makes 5-6-7 and 8索 makes 6-7-8. Two kinds of tile, up to eight copies, which is why this is the wait you want.
Three waits hidden in one long run
Waits
Three sets are plain: 1-2-3 and 4-5-6 of characters and 7-8-9 of dots. The other seven tiles run 2 to 8 in bamboo, and together with the winning tile they have to become two sets and a pair. Split them as 2-3-4 and 5-6-7 and the 8 is left alone, so 8索 wins; as 3-4-5 and 6-7-8, the 2 is alone, so 2索 wins; as 2-3-4 and 6-7-8, the 5 is alone, so 5索 wins. One stretch of bamboo waits on 2, 5 and 8, and the 5 in the middle is the easy one to miss.
Common mistakes
• Stopping at the first wait you find. Many ready hands wait on two or three kinds of tile.
• Missing the pair waits: a lone tile waits for its own pair, and two pairs wait on either one.
• Reading a long run only one way. 2-3-4-5-6-7-8 of one suit waits on 2, 5 and 8, not only on the ends.
• Counting a dead wait. If all four copies of a tile are already visible, in your hand or on the table, it cannot win for you.
Practice now
Below is the app's waits drill at Novice (入門), the free tier: ten sorted hands, each already ready (聽牌), and you pick a tile that wins. It runs on the real game engine, so every answer is checked exactly as the game would check it.
It means your hand is ready: one more tile would complete five sets and a pair. The tiles that would do it are your waits.
Is reading waits different in 16-tile Taiwanese mahjong than in 13-tile mahjong?
The shapes are the same: two-sided, gap, edge, single and two pairs. A 16-tile hand has five sets instead of four, so there are more tiles to sort and more room for long runs that hide extra waits.
What is the best kind of wait?
Usually the one with the most live tiles. A two-sided wait like 6-7 has up to eight winning tiles; a gap, edge or single wait has at most four. A long run such as 2 to 8 in one suit can wait on three kinds.
Can I still win on a tile when all four copies are visible?
No. If all four copies are in your hand or on the table, none is left to complete the hand, so it is not a real wait. The app's Expert tier trains you to spot this.